Although William Pereira first gained national recognition for his movie set designs, including those for the 1942 film “Reap the Wild Wind,” future generations will remember him as the architect of the Transamerica Tower, the Malibu campus of Pepperdine University, and the city of Irvine.

a. including those for the 1942 film “Reap the Wild Wind,” future generations will
b. like those for the 1942 film “Reap the Wild Wind,” future generations
c. like that for the 1942 film “Reap the Wild Wind,” future generations will
d. including that for the 1942 film “Reap the Wild Wind,” future generations will
e. including those for the 1942 film “Reap the Wild Wind,” future generations

The answer mentions that future generations 'will' is correct. I am not sure because the first says that Pereira 'first' gained..which is in the past and therefore the future generations should 'remember' him. Also the Transamerica tower, the malibu campus etc are already built. How can this sentence be in future tense? Any further clarifications will be great.

The "will" refers to remembering him as the architect, not to the construction dates of the buildings. "future generations will remember him as the architect" He will always be the architect - in the past, now, and in the future.

We know this part of the sentence should be in the future because it specifically says future generations.

Note that a sentence can change tenses, as in this case. We start with mention of why he was well-known in the past (first gained...movie set designs) and then the sentence switches tenses to tell us why he will be well-known in the future (future generations will remember him as the architect...). The "although" also signals the contrast to come - he was first known, in the past, for one type of thing but, in future, he will be known for something else (assuming the author's prediction is right!).

p.s. please remember to follow protocol. The subject of your post should be the first 5-8 words of the question itself. Thanks!